The present invention relates to a pig for repairing interior portions of a pipeline comprising cast-iron pipes, and more particularly to a pig for repairing a sealing device in a joint of pipes of a pipeline such as a town gas pipeline or water pipeline. The quality of the sealing device of the gas pipeline deteriorates with laps of time, which causes leakage of gas from the pipeline. Therefore, it is necessary to repair the sealing device of old pipeline.
A method of repairing the sealing device of the joint of the gas pipeline with pigs has been proposed by the inventor. The method uses three pigs connected with each other by ropes at suitable distances. A first space between first and second pigs is filled with plastics having a low viscosity as a permeable material, and a second space between second and third pigs is filled with a puttying material. The pigs are moved in the pipeline passing through a joint. During the movement of pigs, the plastics permeates into a sealing member such as a gasket in a space of the joint, and then the puttying material is charged in a space between adjacent pipes, substituting for the plastics in the space. Thus, the joint is sealed by the puttying material.
In such a method, air in the sealing member must be substituted by the plastics pearmeated therein, and plastics remaining in the space between pipe ends must be substituted by the putting material.